The present invention relates generally to motor vehicle differentials and more particularly to a differential wherein the torque bias between a pair of outputs may be adjusted.
Geared differentials have been a component of motor vehicle drive trains from the earliest designs. In even the earliest vehicles, it became apparent that turning a corner and the wheel speed differences created between the inner and outer driving wheels during such maneuvers must be accommodated by the drive system.
While the standard bevel gear differential has accommodated this wheel speed difference for decades, improvements have occurred. For example, limited slip differentials which utilize a clutch having a preset torque limit prevent independent rotation until the forces acting upon the wheels and torque acting upon the axles exceeds a preset value. This addressed a common shortcoming of open differentials which, without such a feature, would direct drive torque to the tire on the slipperier surface, thereby frequently causing a vehicle to be trapped or stuck unnecessarily in snow, ice or mud.
Typically differentials are constructed with an equal, i.e., 50—50 torque split. This is true whether they are realized in front or rear axles or as an interaxle or center differential. In a center or interaxle differential, differentials have also been configured to provide, for example, a 40–60 torque split or a torque split other than 50—50.
The vast majority of active differentials include a mechanism which transfers torque from the faster rotating output to the slower rotating output. There are situations where it would be desirable to transfer torque from the slower rotating output to the faster rotating output. Those conditions include when wheel slip initially occurs on the rear wheels when in a corner. When turning, the front wheels are turning at a higher average speed than the rear. If the biasing mechanism is applied before the average wheel speed of the rear wheels is greater than the average speed of the front, the results will be counterproductive. The traditional active differential may not have the relative shaft speeds in the proper direction or may have an insignificant relative speed difference, causing the biasing clutches to be ineffective in creating the desired change in vehicle handling or yaw.
The present invention is directed to a differential configuration wherein the torque split between two outputs is adjustable in real time.